An electric drive may be used as source of driving power in a vehicle, such as, for example, an off-road work machine, a highway truck, or an automobile. An electric drive may supplement the driving power provided by an internal combustion engine or the electric drive may provide all of the driving power for the vehicle. Using an electric drive to supplement or replace the internal combustion engine may reduce the emissions generated during the operation of the vehicle. In addition, the electric drive may increase the fuel efficiency of the vehicle.
An electric drive typically includes a source of electrical power and an electric motor that is connected to one or more ground engaging devices on the vehicle. The source of electrical power, which may be, for example, a battery or an engine, provides the power that is used to operate the electric motor to generate an output torque. The output torque is transferred to the ground engaging devices on the vehicle to thereby propel the vehicle.
Some vehicles, such as tracked work machines, may include a differential steering system that is disposed between the electric motor and the ground engaging devices on the vehicle. A differential steering system may include one or more planetary gear assemblies and a steering motor. The differential steering system is operable to change the relative speeds of the ground engaging devices to thereby change the direction of travel of the vehicle. When a ground engaging device on one side of the vehicle is driven at a slower speed than a ground engaging device on the other side of the vehicle, the vehicle will tend to turn towards the slower moving ground engaging device.
In a typical electric drive, such as the electric drive described in U.S. Pat. No. 6,024,182 to Hamada et al., the output torque of an electric motor is transferred from the electric motor to a differential system through a gear transfer system that may include, for example, a bevel or spur gear arrangement. However, the use of a bevel or spur gear arrangement is an inefficient method of transferring the torque of the motor to the ground engaging devices. Some of the torque generated by the electric motor may be lost in the torque transfer. These gear losses decrease the efficiency of the electric drive and the overall efficiency of the vehicle.
The electric drive system of the present invention solves one or more of the problems set forth above.